A132288 Odd palindromes which are semiprimes with an even number of digits.
33, 55, 77, 1111, 1441, 1661, 1991, 3113, 3223, 3443, 3883, 7117, 7447, 7997, 9119, 9229, 9449, 100001, 103301, 104401, 107701, 113311, 115511, 116611, 124421, 125521, 130031, 136631, 139931, 146641, 152251, 157751, 160061, 163361, 164461, 169961, 170071
Offset: 1
Links
- Robert Israel, Table of n, a(n) for n = 1..10000
Programs
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Maple
rev:= proc(n) local L,i; L:= convert(n,base,10); add(L[-i]*10^(i-1),i=1..nops(L)) end proc: f:= proc(m) local A,i,j,k; select(t -> isprime(t/11), [seq(seq(10^(m-1)*i + 10^(m/2)*j + rev(10^(m/2-1)*i+j),j=0 .. 10^(m/2-1)-1),i=[1,3,5,7, 9])]) end proc: seq(op(f(m)),m=2..6,2); # Robert Israel, Jan 05 2025
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PARI
lista(nn) = {for(n=1, nn, if (ismo(n) && (bigomega(n) == 2), print1(n, ", ");););} \\ where ismo is isok in A132285 \\ Michel Marcus, Nov 05 2013
Formula
a(n) = 11*A132287(n).
Extensions
More terms from Michel Marcus, Nov 05 2013
Name edited by Robert Israel, Jan 05 2025
Comments